Histology of Cartilage, Bone and Joints Flashcards
What is cartilage made of?
Chondrocytes
Extracellular matrix
What makes cartilage?
Chondrocytes
What do chondrocytes secrete?
Extracellular matrix
What are the types of cartilage?
Hyaline
Elastic
Fibrocartilage
Which type of cartilage is the most common?
Hyaline
What is the general structure of hyaline cartilage?
Homogenous, amorphous matrix encased in perichondrium
What is the perichondrium?
Thin outer layer of cartilage
What are the properties of hyaline cartilage?
Low friction surface
Lubrication of synovial joints
Distributes applied forces
What are lacunae?
Spaces within extracellular matrix of cartilage
Where are chondrocytes within cartilage?
In lacunae
What does the extracellular matrix of hyaline cartilage consist of?
Mainly type II collagen Proteoglycans = large glycosaminoglycans, including - Chondroitin sulphate - Keratan sulphate - Hyaluronate Chondronectin
What is chondronectin?
Glycoprotein Binds - Collagen - Aggrecans - Integrins
What is elastic cartilage?
Hyaline cartilage with addition of elastin
Where is elastic cartilage found?
Ears
Ear canals
Epiglottis
Larynx
What are the properties of elastic cartilage?
Very flexible
Maintains shape
What does fibrocartilage do?
Binds solid joints
Forms meniscus and intervertebral discs
What is fibrocartilage made of?
Dense connective tissue (type I)
Isolated islands of cartilage
- Type II collagen in matrix
- Dispersed chondrocytes
Does fibrocartilage have a perichondrium?
No
What are the properties of fibrocartilage?
Resists compressive and shearing forces
In which bones is there a marrow cavity?
Long bones
What does the marrow cavity contain?
Bone marrow
Fat
What makes the dense wall of bone?
Compact bone
What makes the “spongy” interior of bone?
Cancellous/trabecular bone
What is the periosteum?
Bone surface covered with thin layer of connective tissue
What are the two layers of the periosteum?
Outer fibrous layer
Inner more cellular layer
What is in the outer fibrous layer of the periosteum?
Fibroblasts
Blood vessels
Collagen
What is in the inner more cellular layer of the periosteum?
Osteoprogenitor cells
What type of bone forms the shaft of the long bone?
Compact bone
What is the structure of compact bone?
Outermost and innermost (lining marrow cavity) part in concentric layers
Rest formed by osteons/Haversian systems
What is an osteon/Haversian system?
Cylindrical modules
What is the organisation of trabecular bone compared to compact bone?
Less organised
What is trabecular bone made of?
Lamellae but not Haversian systems
What are the spaces in trabecular bone like?
Continuous
Full of marrow and blood vessels
What does the medullary cavity contain?
Marrow
What types of marrow are there?
Red
Yellow
When is red marrow present?
Early in life
What is red marrow made of?
Mainly haematopoietic cells
When is yellow marrow present?
Later in life
What is yellow marrow made of?
Mainly fat cells
Does yellow marrow have any haematopoietic cells?
Yes, preserves some
Can become active haematopoietic tissue if needed
What do the blood vessels have instead of capillaries?
Sinusoids
What is the endosteum?
Covering over bone lining marrow cavity
Compare endosteum and periosteum
Endosteum thinner
Both have osteoprogenitor cells
Endosteum has fibrous element
How do arteries supply bones?
At discrete points
Branch in marrow cavity
Supply shaft and ends separately
Periosteum separately supplied
How do nerves supply bones?
Abundant
Follow blood vessels
What is the diaphysis?
Bone shaft
What is the epiphysis?
Bone end
What cells do osteoprogenitor cells develop into?
Osteoblasts
What cells do osteoblasts develop into?
Osteocytes
What cells do osteocytes develop into?
Bone lining cells
What is the origin of osteoprogenitor cells?
Mesenchymal stem cells
What is the origin of osteoclasts?
Granulocyte/macrophage cell origin
What is the usual state of osteoprogenitor cells?
Resting/quiescent
Why do osteoprogenitor cells give rise to new osteoblasts?
Grow/repair bone
Where are osteoprogenitor cells found?
Periosteum
Endosteum
What is the shape of osteoprogenitor cells?
Flattened
Where are osteoblasts found?
On bone surface of both compact and trabecular bone
What do osteoblasts do?
Secrete bone matrix
What is in the bone matrix secreted by osteoblasts?
Type I collagen
Bone matrix proteins
- Ca binding proteins = osteocalcin, osteonectin
- Adhesive proteins = sialoproteins, osteopontin
- Proteoglycans
- Alkaline phosphatase
What are markers of osteoblast activity?
Osteocalcin
Alkaline phosphatase
What shape are osteoblasts?
Active = cuboidal/polygonal Inactive = flattened
What happens to osteoblasts as deposition of matrix occurs?
Become surrounded by matrix > become osteocytes
What happens to some osteoblasts?
Become periosteal/endosteal bone lining cells
What are osteocytes?
Mature bone cells
Surrounded by bone
Where are osteocytes found?
Sit in lacunae
How do osteocytes communicate with each other?
Via canaliculi (not visible with H&E)
What do osteocytes do?
Maintain bone in response to loading
What happens if osteocytes are lost?
Bone resorption
Why can you sometimes see white spaces around osteocytes histologically?
Destroy local bone to free calcium
What is the shape and size of osteoclasts?
Giant multinuclear cells
What do osteoclasts do?
Destroy bone in - Growth - Repair - Normal turnover = remodelling Release calcium
Where are osteoclasts found?
Seal themselves to bone around edge
How do osteoclasts break down bone?
Secrete
- Protons from H2CO3 breakdown
- Proteases
What is a marker of osteoclast activity?
Tartrate-resistant acid phosphatase
What nutrient is bone a major reservoir for?
Calcium
What increases blood calcium?
Osteoclast/osteocyte activity
What decreases blood calcium?
Osteoblast activity
What controls calcium homeostasis?
Hormones from
- Thyroid gland
- Parathyroid gland
What types of bone are laid down during development?
Membranous
Endochondral
What is intramembranous ossification?
Membranous bone forms directly from mesenchyme
Which bones undergo intramembranous ossification?
Skull
Flat bones of face
Mandible
Clavicles
What is endochondral ossification?
Cartilage model of bone produced
Cartilage replaced by bone
Which bones undergo endochondral ossification?
Weight bearing bones
Bones of extremities
What are the steps of endochondral ossification?
- Bone collar forms around diaphysis
- Cartilage beneath collar degenerates
- Blood vessels invade, bring in bone cell progenitors = 1st centre of ossification
- 2nd centre of ossification appears in each epiphysis
- Zones of ossification grow together but leave thin zone of cartilage = growth plate
- Growth plate lost with age
What does the growth plate do?
Enables long bones to grow
When does the growth plate fuse?
21-22 years
What are the zones of the growth plate?
Resting Proliferative Maturation Hypertrophic Ossification
What type of bone is new bone, either during development or repair?
Woven bone
How is woven bone different to compact and trabecular bone?
More cellular
More collagen
No Haversian systems
What cells remodel woven bone?
Osteoclasts
Osteoblasts
How does remodelling occur via Haversian systems?
Osteoclasts make new cavities in bones Along stress axis Blood vessels and endosteum invade Osteoblasts line new space Lay down layer of bone
What are synovial joints?
Joints where bones move freely against each other
What creates the joint space?
Connecting bones outside articular cartilage with synovial membrane
What type of cartilage is articular cartilage?
Hyaline
What are the properties of articular cartilage?
Slippery
Smooth
Resistant to compression
No perichondrium
What is in the synovial space?
Synovial fluid
What does the synovial fluid do?
Lubricates
Provides nutrients
What lines the synovial space?
Synovial membrane
What is the synovial membrane?
Not epithelium
What is the structure of the synovial membrane
No - Basement membrane - Tight junctions - Desmosomes Surface layer = intima - 2-3 cells thick - Mix of fibroblast-like and macrophage-like synoviocytes Sub-intimal layer - Connective tissue
What is synovial fluid made of?
Ultrafiltrate from synovial blood vessels
Proteoglycans
What is the structure of intervertebral discs?
External ring of fibrocartilage = annulus fibrosis Nucleus pulposus - From notochord - Forms gelatinous centre - Type II collagen - Replaced by fibrocartilage by age 20